Alloy formation of Y with Pd investigated by photoemission and electron diffraction

The structure of Pd capped Y films for an application as a switchable mirror was studied. The surface structures are investigated by reflecting high energy electron diffraction and Auger electron spectroscopy. The alloy formation between Y and Pd leads to different structural and electronic properties of the surface, which are compared to the switching behavior of the underlying Y film when exposed to hydrogen. The electronic structure of the intermetallic compound YxPd1-x(0 <x <0.25) was studied by angular-resolved ultraviolet photoemission spectroscopy. The samples were prepared by Y deposition on Pd (111) surfaces of epitaxial films. The electronic structure of the alloy is discussed in the framework of a qualitative tight-binding approach. The reactivity of the Y-Pd alloy surfaces is estimated using the chemisorption model of Hammer and Norskov [Nature 376, 238 (1995)]. We show that exposure to air leads to an oxygen induced surface segregation of the Y-Pd alloy, which hinders hydrogen adsorption. (C) 2001 American Institute of Physics.